<style>
    .stars {
        background-color: white;
        height: 30px;
        width: 30px;
        border-radius: 50%;
        animation-iteration-count: infinite;
    }

    .star-1 {
        margin-top: 15%;
        margin-left: 60%;
        animation-duration: 1s;
        animation-name: twinkle;
    }

    .star-2 {
        margin-top: 25%;
        margin-left: 25%;
        animation-duration: 0.9s;
        animation-name: twinkle;
    }

    .star-3 {
        margin-top: 10%;
        margin-left: 50%;
        animation-duration: 1.1s;
        animation-name: twinkle;
    }

    @keyframes twinkle {
        20% {
            transform: scale(0.5);
            opacity: 0.5;
        }
    }

    #back {
        position: fixed;
        padding: 0;
        margin: 0;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
        background: linear-gradient(black, #000099, #66c2ff, #ffcccc, #ffeee6);
    }
</style>

<div id="back"></div>
<div class="star-1 stars"></div>
<div class="star-2 stars"></div>
<div class="star-3 stars"></div>